STEM-22. TUMOR TREATING FIELDS REPROGRAM GLIOBLASTOMA STEM CELLS TOWARD A PROINFLAMMATORY AND IMMUNOSTIMULATORY PHENOTYPE

Abstract Glioblastoma stem cells (GSCs) are critical drivers of immune evasion and therapeutic resistance. Tumor Treating Fields (TTFields), a non-invasive modality delivering low-intensity alternating electric fields, have demonstrated clinical benefit in glioblastoma. However, their immunomodulatory effects on GSCs remain poorly understood. In this study, we investigated the impact of TTFields on the immunological phenotype of GSCs by integrating cytokine secretion profiling and transcriptomic analysis. GSCs from multiple patient-derived lines were exposed to TTFields (200 kHz, 72 hours), followed by cytokine array profiling of over 100 soluble factors and RNA sequencing. TTFields induced a profound shift in the cytokine landscape. Proinflammatory mediators such as IL-1β, IL-6, TNF-α, IL-12p70, and IL-31 were upregulated. Notably, several immune-activating cytokines were induced de novo under TTFields, including IL-15, IL-34, IP-10, and PF4, which were undetectable in control conditions. In contrast, immunosuppressive and tumor-promoting cytokines such as Angiopoietin-1, Fas Ligand, CD30, and DPPIV were downregulated. Transcriptomic profiling revealed concordant changes, with significant upregulation of immune-related genes including MAFB, A2M, and FOXA3, all of which are involved in monocyte/macrophage differentiation, immune regulation, and cytokine signaling. Together, these findings demonstrate that TTFields reprogram GSCs both at the transcriptional and secretory levels toward a proinflammatory and immunostimulatory state. This dual-layered immune activation suggests that TTFields may enhance glioblastoma stem cells immunogenicity and provide a mechanistic rationale for combining TTFields with immunotherapies targeting myeloid cells or checkpoint pathways in glioblastoma.